Conveyance of electrically charged sheets

ABSTRACT

An apparatus wherein charged sheets of electrophotographic paper are conveyed from a charger to an exposure position and from the exposure position to a liquid developer by a series of endless belts driven by rollers. To maintain the paper in contact with the belts during passage around a roller a guide sheet of polytetrafluorethylene is biassed towards the belts. The paper passes between the belt and the guide sheet with its charged, photoconductive layer contacting the guide sheet and its base layer contacting the belts.

United States Patent Inventor Martin R. P. Scib l0 Lodge Drive, The Ryde, Hatfield, Hertfordshlre, England Appl. No 753,298

Filed Aug. 16, 1968 Patented June 8, I971 CONVEYANCE 0F ELECTRICALLY CHARGED SHEETS 7 Claims, 1 Drawing Fig.

US. Cl 271/63, 271/75 Int. Cl B65h 29/16 Field of Search 271/3, 8, 45, 63, 68, 75; 198/160 References Cited UNITED STATES PATENTS 2/1938 Ochsenbein 27 l/45X 2,153.154 4/1939 Nivison 271/8 2,920,748 l/l960 Heywood l98/l60X 3,272,504 9/1966 Schnoebelen 271/68 Primary Examiner-Edward A. Sroka Attorney-Delio and Montgomery ABSTRACT: An apparatus wherein charged sheets of electrophotographic paper are conveyed from a charger to an exposure position and from the exposure position to a liquid developer by a series of endless belts driven by rollers. To maintain the paper in contact with the belts during passage around a roller a guide sheet of polytetrafluorethylene is biassed towards the belts. The paper passes between the belt and the guide sheet with its charged, photoconductive layer contacting the guide sheet and its base layer contacting the belts.

PATENTED JUN 81971 INVENTOR Mavhn Rqqmond PercwM 5lb A TORNEYS CONVEYANCE OF ELECTRICALLY CHARGED SHEETS BACKGROUND OF THE INVENTION This invention relates to a conveying means for electrically charged sheets of electrophotographic paper.

In electrostatic developing and printing apparatus and electrostatic charge is formed on a photoconductive layer on one surface of an electrophotographic paper and an optical image of a predetermined object is focused on to the charged surface by optical projection means. The charge leaks away from those areas of the charged surface which are subjected to electromagnetic radiation and an electrostatic charge image, corresponding to the photographic image projected by the optical projection means, is thereby formed. To develop the electrostatic image the sheet is suitably passed through a developing bath containing a liquid suspension of black, charged toner particles in an insulating liquid such as paraffin. The charged particles adhere to the charged or uncharged areas of the sheet, according to their polarity, and thereby produce a positive or negative print of the original photographic image. Fixing is effected by drying the sheet to remove excess paraffin.

In electrostatic apparatus of the above form it is important that the charge distribution on a sheet shall not be distributed during transport of a sheet from an initial charging means to a viewing table wherein the sheet is exposed and during transport of the exposed sheet from the table to developing means.

SUMMARY OF THE INVENTION The present invention consists in means for conveying a charged sheet of electrophotographic paper along a predetermined path comprising driving element means adapted to engage an electrically conductive base of the sheet and to apply to the sheet a frictional drive which urges the sheet along the path, a guide sheet, and means for urging the guide sheet towards the driving element means and into engagement with a photoconductive layer of a sheet engaged by the driving element means, the guide sheet maintaining the'sheet of paper in engagement with the driving element meansand being formed of an insulating material adapted to apply low frictional resistance to movement of the sheet of paper along the path and to efiect a small change in the distribution of electrical charge thereon.

Preferably the polytetrafluorethylene.

The means for urging the guide sheet towards the driving element means may comprise a backing of foam plastics or the like resilient material which contacts the surface of the guide sheet remote from driving element means.

The driving element means may comprise a'driving roller and at least one endless belt which is driven by the roller.

guide sheet is formed of BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, by way of example, with reference to the accompanying drawing, which shows a side elevation, partly in section, of an apparatus according to the invention.

Referring to the drawing, the present apparatus includes a store for sheets of electrophotographic paper and means for conveying sheets individually from the store to a pair of driving rollers l at the entrance to a charger 3. Within the charger 3 an electrostatic charge is induced in a photoconductive layer of each sheet, there being a positive or negative charge on the outer surface of the layer according to the polarity of the electrical connections to the charger.

From the charger 3 a sheet is driven to an exposure position on a viewing table 5, where an electrostatic image is formed by exposing the photoconductive layer of the sheet to light from an optical projection system, not shown in the drawings. Finally, after exposure to the light, the sheet is conveyed to liquid developing means 7.

As indicated in the drawing, the table 5 includes a top 9 which is upwardly and rearwardly inclined from front to rear, right to left as shown in the drawing, and a pair of side plates 11 which depend from the top 9.

Mounted on the table 5 are driving means 13 including a driving roller 15 at the upper edge of the top 9, a corresponding idler roller 17 at the lower edge, and two further idler rollers 19 and 21. Each roller is joumaled in bearings respectively mounted inside plates 11 of the table and extends parallel with the upper and lower edges of the table top 9.

Engaging the rollers 15 to 21 of the driving means 13 are a series of endless belts 23, each having an upper run in flatwise engagement with the upper surface of the top 9. These belts 23 are made of terylene coated with a silicone skim.

At the edge of the table top 9 a front cover plate 27 is mounted on the side plates 11 by respective hinges 25 which allow pivotal movement of the cover plate about a horizontal axis parallel with the axis of the rollers 15 to 21. The cover plate 27 is urged in an anticlockwise direction about its pivotal axis by a pair of springs 31, each spring having one end thereof secured to a lug 33 on the cover plate and another end thereof secured to a side plate 11.

A backing 35 of foam plastics material is provided on an inner surface of the cover plate 27, facing the belts 23.

Also mounted on the cover plate 27 is a sheet 37 of polytetrafluoroethylene, which serves to guide a sheet of paper from the charger 3 into engagement with the belts 23 and then to maintain the sheet in contact with the belts during its travel on to the table top 9. A lower edge of the guide sheet 37 is secured to the cover plate 27 and from this edge the sheets extends upwardly and forwardly of the table, into engagement with the belts 23, and then upwardly and rearwardly between tee belts 23 and the backing 35. The upper section of the guide sheet 37 is urged towards the belts 23 and roller 17 by the above-mentioned springs 31 acting on the cover plate 27 and backing 35.

At the upper edge of the table top 9 a further guide sheet 39 of polytetrafluoroethylene is urged towards the belts 23 and driving roller 15 by a series of springs 41 of beryllium-copper, each spring having a backing 43 of foam plastics material thereon.

in operation of the present apparatus a sheet of paper enters the charger 3 with its photoconductive layer uppermost and its base layer lowermost. As the leading edge of the sheet emerges from the charger 3 the trailing section of the sheet is still engaged by the driving rollers l, which continue to drive the sheet forwardly into engagement with a lower section of the guide sheet 37. The sheet 37 guides the leading edge of the paper upwardly and forwardly into engagement with the belts 23 and the paper is then driven around a section of the roller 17, engaged between the belts 23 and the guide sheet 37, and on to the table top 9. It will be appreciated that the base layer of the paper contacts the belts 23 and the photoconductive layer contacts guide sheet 37.

When the paper has reached a predetermined central position on the table top 9 the drive means for the roller 15 are disconnected and the paper remains stationary during exposure to light from the optical projection means.

After exposure the drive means are again connected to the roller 15, whereupon the paper is driven upwardly and rearwardly across the table top 9 and then downwardly and rearwardly, between the guide sheet 39 and the belts 23, to the liquid developing means 7.

It is found that the guide sheets 37 and 39 serve to maintain a charged sheet of paper in engagement with the belts 23 without imparting a significant frictional resistance to the advance of the paper or a significant change in the charge distribution thereon. The belts may be made of a fabric impregnated with an electrically conductive resin.

lclaim:

1. Means for conveying a charged sheet of electrophotographic paper along a predetermined path comprising driving element means adapted to engage an electrically conductive base of the sheet and to apply to the sheet a frictional drive which urges the sheet along the path, a guide sheet, and means for urging the guide sheet towards the driving element means and into engagement with a photoconductive layer of a sheet engaged by the driving element means, the guide sheet maintaining the sheet of paper in engagement with the driving ele ment means and being formed of an insulating material adapted to apply low frictional resistance to movement of the sheet of paper along the path and to effect only a small change in the distribution of electrical charge thereon, said means for urging the guide sheet towards the driving element means comprising a backing of foam plastics or the like resilient material which contacts the surface of the guide sheet remote from the driving clement means.

2. Conveying means as claimed in claim 1, wherein the guide sheet is formed of polytetrafluorethylene.

3. Conveying means as claimed in claim 1, wherein the means for urging the guide sheet towards the driving element means further comprise a movable cover plate having the said backing of foam plastics material secured thereto, and means for biassing the cover plate in a predetermined direction so that the said backing of foam plastics material and the guide sheet are urged towards the driving element means.

4. Conveying means as claimed in claim 1, wherein the driving element means comprise a driving roller and at least one endless belt which is driven by the belt.

5. Conveying means as claimed in claim 4, wherein the driving belt is made of terylene coated with a silicone skin.

6. Conveying means as claimed in claim 4, wherein the driving belt is made of a fabric impregnated with an electrically conductive resin.

7. Means for conveying a charged sheet of electrophotographic paper along a predetermined path comprising driving element means adapted to engage an electrically conductive base of the sheet and to apply to the sheet a frictional drive which urges the sheet along the path, a guide sheet, and means for urging the guide sheet towards the driving element means and into engagement with a photoconductive layer of a sheet engaged by the driving element means, the guide sheet maintaining the sheet of paper in engagement with the driving element means and being formed of an insulating material adapted to apply low frictional resistance to movement of the sheet of paper along the path and to effect only a small change in the distribution of electrical charge thereon, said driving element means comprising at least one endless belt moving over and under said table and about rollers at each end of said table, said guide sheet being formed in an arcuate shape and disposed in operative relation with one of said rollers so that a sheet is fed to said driving element means between said guide sheet and said one of said rollers. 

1. Means for conveying a charged sheet of electrophotographic paper along a predetermined path comprising driving element means adapted to engage an electrically conductive base of the sheet and to apply to the sheet a frictional drive which urges the sheet along the path, a guide sheet, and means for urging the guide sheet towards the driving element means and into engagement with a photoconductive layer of a sheet engaged by the driving element means, the guide sheet maintaining the sheet of paper in engagement with the driving element means and being formed of an insulating material adapted to apply low frictional resistance to movement of the sheet of paper along the path and to effect only a small change in the distribution of electrical charge thereon, said means for urging the guide sheet towards the driving element means comprising a backing of foam plastics or the like resilient material which contacts the surface of the guide sheet remote from the driving element means.
 2. Conveying means as claimed in claim 1, wherein the guide sheet is formed of polytetrafluorethylene.
 3. Conveying means as claimed in claim 1, wherein the means for urging the guide sheet towards the driving element means further comprise a movable cover plate having the said backing of foam plastics material secured thereto, and means for biassing the cover plate in a predetermined direction so that the said backing of foam plastics material and the guide sheet are urged towards the driving element means.
 4. Conveying means as claimed in claim 1, wherein the driving element means comprise a driving roller and at least one endless belt which is driven by the belt.
 5. Conveying means as claimed in claim 4, wherein the driving belt is made of terylene coated with a silicone skin.
 6. Conveying means as claimed in claim 4, wherein the driving belt is made of a fabric impregnated with an electrically conductive resin.
 7. Means for conveying a charged sheet of electrophotographic paper along a predetermined path comprising driving element means adapted to engage an electrically conductive base of the sheet and to apply to the sheet a frictional drive which urges the sheet along the path, a guide sheet, and means for urging the guide sheet towards the driving element means and into engagement with a photoconductive layer of a sheet engaged by the driving element means, the guide sheet maintaining the sheet of paper in engagement with the driving element means and being formed of an insulating material adapted to apply low frictional resistance to movement of the sheet of paper along the path and to effect only a small change in the distribution of electrical charge thereon, said driving element means comprising at least one endless belt moving over and under said table and about rollers at each end of said table, said guide sheet being formed in an arcuate shape and disposed in operative relation with one of said rollers so that a sheet is fed to said driving element means between said guide sheet and said one of said rollers. 